The present invention relates to information transfer methods and apparatus and, more particularly, to a novel method for transmitting information at any desired bandwidth while suppressing interference from harmonics of a system-wide signal, and novel apparatus for practicing the method.
Data transmission systems are known for operation in a hostile environment having at least one potentially-interfering signal. The system disclosed in U.S. Pat. Nos. 3,944,723 (issued Mar. 16, 1976); 3,973,087 and 3,973,240 (both issued Aug. 3, 1976), all assigned to the assignee of the present invention, provides data communication utilizing a commercial power line as the transmission medium, wherein harmonics of the power transmission frequency (generally 60 Hz. in the United States) may appear within the passband assigned to a data carrier and interfere with the data transmitted thereon. The rate at which data may be transmitted has been generally restricted to relatively low rates in a system having harmonics of a system-wide signal. Several methods are known for increasing the data bandwidth, and hence the data rate; one such method comprises phase locking a data carrier at a frequency exactly between harmonics of a system-wide signal subject to frequency change and modulation of the data carrier at a baud equal to an exact submultiple of the frequency of the system-wide signal, as disclosed in pending U.S. application Ser. No. 722,551, filed Sept. 13, 1976 and assigned to the assignee of the present invention. This and similar techniques do not allow relatively wide bandwidth, and hence high data rate, to be achieved by data transmission using a single carrier (which single carrier technique does not require the additional equipment required for frequency multiplex transmission schemes). A method and apparatus using wide communication bandwidth in a single carrier system having a system-wide potentially interfering signal, and with suppression of harmonic interference therefrom, is desirable.